Porous ceramic articles are widely used as adsorbents, catalyst supports, filters, burner elements, etc. The usefulness of a porous ceramic article for a particular purpose is at least partially related to the pore morphology of the ceramic article. Consequently, there is a constant desire for ceramic articles having new and useful pore morphologies as well as for inexpensive methods for producing such articles.
Electrophoresis is a process whereby particles in a liquid suspension are drawn toward an electrode when an electric field is applied across the suspension. The direction and rate that a particle travels depends on the charge present on the particle's surface, the conditions of the medium in which the particle is suspended, conditions at the electrode(s), the electrical potential applied and the characteristics of the particle itself.
Often, the surface charge on a particle can be varied by changes in the pH, the concentration of electrolyte in the medium and/or by addition of a polyelectrolyte adapted to interact with the particle surface.
In the past, electrophoresis has been used to produce alumina coatings on stainless steel plates by Choudhary et al., Trans. J. Br. Ceram. Soc. 81, pp. 189-193 (1982). Choudhary et al. employed an aqueous suspension containing the alumina particles.
Electrophoresis has also been used to deposit enamel coatings from various suspensions onto workpieces. An example of enamel deposition is disclosed in U.S. Pat. No. 4,466,871 to Kaup et al.
Some have used electrophoresis to produce three-dimensional ceramic shapes such as described by Heavens in the article "Manufacture of Beta Alumina Shapes by Electrophoretic Deposition, " Brit Ceram. Proc. No. 38, Davidge, R. W. ed., pp. 119-126 (1986). Most of the three-dimensional shapes formed have been deposited on relatively large diameter electrodes (e.g., greater than 1 inch wide). Most of these prior art processes have involved the use of organic suspension media as opposed to aqueous media. Aqueous media have been avoided (except in the area of thin film coatings) because of problems caused by hydrogen evolution at the cathode or oxygen evolution at the anode due to electrolysis of water.